Specify which Fog storage drivers are imported by default in backup_restore.md

doc/raketasks/backup_restore.md

@@ -81,8 +81,11 @@ Deleting old backups... [SKIPPING]
 Starting with GitLab 7.4 you can let the backup script upload the '.tar' file it creates.
 It uses the [Fog library](http://fog.io/) to perform the upload.
-In the example below we use Amazon S3 for storage.
-Fog also supports [other storage providers](http://fog.io/storage/).
+In the example below we use Amazon S3 for storage, but Fog also lets you use
+[other storage providers](http://fog.io/storage/). GitLab
+[imports cloud drivers](https://gitlab.com/gitlab-org/gitlab-ce/blob/30f5b9a5b711b46f1065baf755e413ceced5646b/Gemfile#L88)
+for AWS, Azure, Google, OpenStack Swift and Rackspace as well. A local driver is
+[also available](#uploading-to-locally-mounted-shares).
 For omnibus packages: